Intervertebral disc prosthesis

ABSTRACT

The present invention relates to an intervertebral disk prosthesis comprising at least three parts including a first plate, referred to as the upper plate ( 1 ), a second plate, referred to as the lower plate ( 2 ), and a core ( 3 ), the upper surface of the core ( 3 ) being in contact with at least part ( 10 ) of the lower surface of the upper plate ( 1 ) and the lower surface of the core ( 3 ) being in contact with at least part of the upper surface of the lower plate ( 2 ), and the lower plate ( 1 ) being movable at least with respect to the core ( 3 ), characterised in that there are cooperation means between the lower to plate ( 2 ) and the core ( 3 ), so as to limit or eliminate translation movements of the core ( 3 ) with respect to the lower plate ( 2 ) along an axis substantially parallel to the lower plate ( 2 ), and to limit or eliminate rotation movements of the core ( 3 ) with respect to the lower plate ( 2 ), around an axis substantially perpendicular to the lower plate ( 2 ), the planes passing through the upper ( 1 ) is and lower ( 2 ) plates forming a substantially constant angle.

The present invention relates to an intervertebral disk prosthesis,intended to substitute the fibrocartilaginous disks joining thevertebrae in the spinal column, particularly on the cervical spine.

Various types of prosthesis are known in the prior art. Some of theseprostheses, either because they are made of compressible material orbecause they allow excessive movement of the different constituent partsof the prosthesis with respect to each other, may induce relativelyeasily the ejection of at least one part of the prosthesis outside thevertebrae, which is not desirable for the patient.

The purpose of the present invention is to remedy some drawbacks of theprior art by proposing a simple intervertebral disk prosthesis whichmakes it possible to limit the movements of the different constituentparts of the prosthesis with respect to each other.

This purpose is achieved by an intervertebral disk prosthesis comprisingat least three parts including a first plate, referred to as the upperplate, a second plate, referred to as the lower plate, and a core, theupper surface of the core being in contact with at least part of thelower surface of the upper plate and the lower surface of the core beingin contact with at least part of the upper surface of the lower plate,and the lower plate being movable at least with respect to the core,characterised in that there are cooperation means between the lowerplate and the core, so as to limit or eliminate translation movements ofthe core with respect to the lower plate, along an axis substantiallyparallel to the lower plate, and to limit or eliminate rotationmovements of the core with respect to the lower plate, around an axissubstantially perpendicular to the lower plate, the planes passingthrough the upper and lower plates forming a substantially constantangle.

According to another feature, the lower plate comprises male meanscooperating with female means of the core.

According to another feature, the lower plate comprises female meanscooperating with male means of the core.

According to another feature, the angle is obtained in that the coreforms an acute angle in the front-rear direction.

According to another feature, the same plates can be assembled withcores of different thicknesses.

According to another feature, the angle between the upper and lowerplates is between 0° and 15°.

According to another feature the core is movable with respect to theupper and/or lower plates, which makes it possible to compensate forpositioning defects of the three parts of the prosthesis with respect toeach other.

According to another feature, at least part of the lower surface of theupper plate is concave and complementary to the upper surface of thecore.

According to another feature, the dimensions of each male means areslightly less than those of each female means so as to enable a slightclearance between the core and the lower plate.

According to another feature, the dimensions of each male means aresubstantially the same as those of each female means so as to preventany clearance between the core and the lower plate.

According to another feature, the male means of the lower plate are twopins curved towards the inside of the prosthesis and located oppositeeach other on two edges of the prosthesis, and in that the female meansof the core are two recesses.

According to another feature, at least one of the pins is replaced by alug equipped with a drilling whereon a tag is fixed using a dowelentering the drilling.

According to another feature, the male means of the lower plate are twodowel pins located in the vicinity of the centre of the lower plate, andin that the female means of the core are two wells.

According to another feature, the male means of the lower plate are twowalls located opposite each other in the vicinity of two edges of theprosthesis, and in that the female means of the core are recesses.

According to another feature, the male means of the lower plate are arib located at the centre of the prosthesis, and in that the femalemeans of the core are a groove.

According to another feature, the core is made of polyethylene.

According to another feature, the lower plate comprises one or moreopenings in the vicinity of its front side, provided to receiveprosthesis anchoring means in a vertebra.

According to another feature, the opening of the lower plate isrectangular, and in that the anchoring means consist of a body, formingan acute angle with the lower plate, and a head.

According to another feature, the openings of the lower plate arecircular, and in that the anchoring means are nail-shaped.

According to another feature, the upper plate is convex on at least partof its upper surface to fit into the shape of the vertebrae.

Other features and advantages of the present invention will be seen moreclearly upon reading the description below, with reference to theappended figures, wherein:

FIGS. 1 a and 1 b respectively represent a bottom view and a perspectivebottom view of the upper plate according to one embodiment,

FIGS. 2 a and 2 b respectively represent a top view and a perspectivetop view of the lower plate according to one embodiment,

FIGS. 3 a and 3 b respectively represent a top view and a perspectivetop view of the core according to one embodiment,

FIGS. 4 a and 4 b respectively represent a perspective top view and aside view of the intervertebral disk prosthesis according to theembodiment of FIGS. 1 a, 1 b, 2 a, 2 b, 3 a and 3 b,

FIGS. 5 a and 5 b respectively represent a side view and a sectionalview along the plane D-D of FIG. 5 a of the intervertebral diskprosthesis according to a second embodiment,

FIG. 6 a represents a side view of the intervertebral disk prosthesisaccording to a third embodiment,

FIGS. 6 b and 6 d represent a sectional view along the plane A-A of FIG.6 a, the core having, respectively, a slight clearance and no clearancewith respect to the lower plate,

FIGS. 6 c and 6 e represent a sectional view along the plane B-B ofFIGS. 6 b and 6 d, respectively, of the intervertebral disk prosthesis,

FIGS. 7 a and 8 a respectively represent a top view and perspectivebottom view of the lower plate according to two other embodiments,

FIGS. 7 b and 8 b respectively represent a perspective side view and aperspective top view of the lower plate of FIGS. 7 a and 8 a,respectively, wherein prosthesis anchoring means are inserted accordingto two different embodiments,

FIG. 9 a represents a top view of the lower plate according to a fourthembodiment,

FIG. 9 b represents a sectional view of the lower plate along the planeplan C-C of FIG. 9 a,

FIGS. 10 a and 10 b respectively represent a rear and side view of theupper plate according to another embodiment.

The intervertebral disk prosthesis according to the invention isconstituted of an upper plate 1 which is articulated with respect to alower plate 2 by means of a core 3, as can particularly be seen in FIGS.4 a, 4 b, 5 a and 6 a. One advantage of the prosthesis according to theinvention is that it comprises simple parts which can be designed sothat the prosthesis is fitted on the cervical spine.

The upper plate 1, particularly visible in FIGS. 1 a and 1 b, isslightly concave on at least part 10 of its lower surface, so as to fitwith the slightly convex upper surface of the core 3. The upper surfaceof the core 3 is complementary to the concave part 10 of the upper plate1, enabling movement between the upper plate 1 and the core 3.

In an alternative embodiment, part of the upper surface of the upperplate 1 is convex, as shown in FIGS. 10 a and 10 b, in order to fitbetter onto the vertebra whereon the prosthesis is to be fitted, thebottom of the vertebrae being concave. In this case, the convex part ofthe upper plate 1 is located in the front part of the upper plate, ascan particularly be seen in FIG. 10 b.

The lower plate 2 is substantially plane. In effect, its lower surfacedoes not need to be convex or concave since the top of the vertebrae issubstantially flat. In the embodiment of FIGS. 2 a, 2 b, 7 a and 8 a,the lower plate 2 comprises two pins 20 located opposite, each other ontwo substantially parallel edges 21, 22 of the lower plate 2. Each pin20 is curved towards the inside of the prosthesis and can thus enterrecesses 30 located on the core 3. The core 3, particularly visible inFIGS. 3 a and 3 b, comprises a substantially plane lower surface,provided to fit onto the lower plate 2. The core 3 is thin (for example3 mm thick) for a cervical prosthesis or thicker (for example 15 mm) fora lumbar prosthesis.

In the embodiment of FIGS. 3 a, 3 b, 4 a and 4 b, the dimensions of eachrecess 30 of the core 3 are slightly greater than those of each pin 20of the lower plate 2 so as to limit the clearance of the core 3 withrespect to the lower plate 2, both in translation along an axissubstantially parallel with the lower plate 2, and in rotation around anaxis substantially perpendicular to the lower plate 2. The movementbetween the upper plate 1 and the core 3, as well as the clearance ofthe core 3 with respect to the lower plate 2, thus enable the patient tomove and, if required, compensate for prosthesis positioning defects.This clearance also offers the advantage of preventing premature weardue to the stress applied to the prosthesis.

In the embodiment of FIGS. 5 a and 5 b, the dimensions of each recess 30of the core 3 are substantially the same as those of each pin 20 of thelower plate 2, so as to prevent any clearance of the core 3 with respectto the lower plate 2, both in translation and rotation. In the lattercase, the only movement of the prosthesis authorised is that of theupper plate 1 with respect to the core 3.

In the embodiment in FIGS. 9 a and 9 b, one of the pins 20 is replacedby a lug equipped with a drilling 200. A tag 23 fixes on the lug bymeans of a dowel 24 entering the drilling 200. In an alternativeembodiment, both pins are replaced by a lug whereon a tag 23 is fixed.

In the embodiment of FIGS. 6 a, 6 b, 6 c, 6 d and 6 e, the lower plate 2does not comprise any pins 20 but two dowel pins 25 located in thevicinity of the centre of the lower plate 2. In this case, the core 3,by complementarity, does not comprise any recesses 30, but two wells 35under its lower surface. The dimensions of the dowel pins 25 of thelower plate 2 and of the wells 35 of the core 3 are such that, in thealternative embodiment represented in FIGS. 6 b and 6 c, a slightclearance in translation and rotation is permitted, and in thealternative embodiment represented in FIGS. 6 d and 6 e, no clearance ispermitted.

In another embodiment, not shown, the lower plate 2 comprises a rib onits upper surface and no pins 20 or dowel pins 25. The core 3, bycomplementarity, comprises a groove under its lower surface. Thedimensions of the rib of the lower plate and the groove of the core aresuch that, in one alternative embodiment, a slight clearance intranslation and rotation is permitted, and in another alternativeembodiment, no clearance is permitted.

In another embodiment not shown, the lower plate 2 comprises, instead ofthe pins 20, two walls, arranged opposite each other, in the vicinity oftwo substantially parallel edges 21, 22 of the lower plate, but furtherin the prosthesis than the pins 20. The core 3 comprises complementaryrecesses with respect to the walls. The dimensions of each recess of thecore in this embodiment are, either slightly greater, or substantiallythe same as those of each wall of the lower plate, so as to enable aslight clearance in translation and rotation or not.

In a further embodiment not shown, the female components are located onthe lower plate and the male components on the core.

The intervertebral disk prosthesis according to the inventionparticularly makes it possible to correct lordosis defects and to addlordosis to the spine, for example the cervical spine. Therefore, thepresence of an acute angle in the front-rear direction F, FIG. 4 b,between the upper plate 1 and the lower plate 2 of the prosthesis isnecessary. For example, this angle is between 0° and 15°. To adjust theangle required according to the patient, it is simply necessary toselect a core 3 with a suitable angle between the mean planerepresenting its upper surface and the plane passing through its lowersurface.

When the female components are located on the lower plates and the malecomponents on the core, the lordotic core, in that it forms an acuteangle in the front-rear direction, may then be integral with the plateby a projection entering a cavity or opening of the lower plate.

The inclination of the prostheses known in the prior art is obtained,either by the shape of the upper plate, when the core is flat, or by theposition of the upper plate with respect to the core, when said core isconvex. With respect to the first case of the prior art mentioned here,the machining of the prosthesis according to the present invention ismore economical since the core is composed of a less expensive material(for example, polyethylene) than that composing the plates. With respectto the second case of the prior art mentioned here, the core of thepresent invention is not liable to be ejected outside the prosthesissince the angle between the plates is substantially constant when theprosthesis is in place.

If surgeons require a determined lordosis for one patient, they willselect a core 3 allowing no clearance with respect to the lower plate 2.On the other hand, if they simply require the lordosis to remain withina range of values, they will select a core allowing a slight clearancein translation and rotation with respect to the lower plate 2.

The intervertebral disk prosthesis according to the invention may, inone alternative embodiment, represented in FIGS. 7 a, 7 b, 8 a and 8 b,be anchored in the spinal column to prevent the prosthesis frommigrating under the effect of the transversal resultant of the forceexerted by the spinal column on the prosthesis in place, which increaseswith the lordosis. In this case, the lower plate 2 comprises one or moreopenings 28, 29 located in the vicinity of the rear side of theprosthesis, making it possible to receive anchoring means 4, 5.

In this way, in the case of FIGS. 7 a and 7 b, the opening 28 of thelower plate 2 is rectangular and the anchoring means 4 is constituted ofa body 40 and a head 41. The dimensions of the head 41 are slightlygreater than those of the opening 28 of the lower plate 2, such that,once the anchoring means 4 are in place in a vertebra, the lower plate 2is sandwiched between the head 41 of the anchoring means 4 and saidvertebra. An angle, less than or equal to 90°, is comprised between thebody 40 of the anchoring means 4 and the lower plate 2.

In the case of FIGS. 8 a and 8 b, two circular openings 29 are comprisedin the lower plate 2 and the anchoring means 5 are nail-shaped, with ahead of greater dimensions than those of the openings 29 to make itpossible to sandwich the lower plate 2 between the head of the anchoringmeans 5 and the vertebra whereon the prosthesis is anchored.

It should be clear to those skilled in art that the present inventionenables embodiments in numerous other specific forms without deviatingfrom the scope of the invention as claimed. Consequently, the presentembodiments must be considered as illustrations, but may be modified inthe field defined by the scope of the attached claims, and the inventionmust not be limited to the details given above.

1. Intervertebral disc prosthesis comprising an upper plate, a lowerplate, and a core, a curved upper surface of the core being in contactwith at least part of a curved lower surface of the upper plate and alower surface of the core being in contact with at least part of anupper surface of the lower plate with an angle between respective planesof the upper and lower plates being obtained by the core having an acuteangle in a front-rear direction, and the upper plate being moveable atleast with respect to the core and the core being movable in translationand rotation with respect to the lower plate, and in which there arecooperation means not located in the middle of the core between thelower plate and the core, so as to limit translation movements of thecore with respect to the lower plate around an axis substantiallyparallel to the lower plate when the intervertebral disc prosthesis isassembled, and to limit or eliminate rotation movements of the core withrespect to the lower plate around an axis substantially perpendicular tothe lower plate when the intervertebral disc prosthesis is assembled, inwhich the lower plate comprises male means cooperating with female meansof the core and the male means of the lower plate are two pins curvedtowards the inside of the prosthesis and located opposite each other ontwo edges of the prosthesis, and in that the female means of the coreare two recesses.
 2. Intervertebral disc prosthesis according to claim1, in which the lower plate and the upper plate are assembled with asecond core rather than the core and the second core has a thicknessthat differs from the thickness of the core.
 3. Intervertebral discprosthesis according to claim 2, in which the angle between the upperand lower plates is between 0° and 15°.
 4. Intervertebral discprosthesis according to claim 1, in which the core is movable withrespect to the upper and/or lower plates, to compensate for relativepositioning defects between the upper plate, the lower plate and thecore of the prosthesis.
 5. Intervertebral disc prosthesis according toclaim 1, in which at least part of the lower surface of the upper plateis concave and complementary to the upper surface of the core. 6.Intervertebral disc prosthesis according to any one of claim 1, in whichthe dimensions of each male means are less than those of each femalemeans so as to enable a slight clearance between the core and the lowerplate.
 7. Intervertebral disc prosthesis according to any one of claim1, in which the dimensions of each male means are substantially the sameas those of each female means so as to inhibit clearance between thecore and the lower plate.
 8. Intervertebral disc prosthesis according toclaim 1, in which at least one of the pins is replaced by a lug equippedwith a drilling whereon a tag using a dowel entering the drilling. 9.Intervertebral disc prosthesis according to claim 1, in which the coreis made of polyethylene.
 10. Intervertebral disc prosthesis according toclaim 1, in which the lower plate comprises one or more openings alongits front side, provided to receive prosthesis anchoring means in avertebra.
 11. Intervertebral disc prosthesis according to claim 10, inwhich the opening of the lower plate is rectangular, and in which theanchoring means comprise a body, forming an acute angle with the lowerplate, and a head.
 12. Intervertebral disc prosthesis according to claim10, in which the openings of the lower plate are circular, and in whichthe anchoring means are nail-shaped.
 13. Intervertebral disc prosthesisaccording to claim 1, in which the upper plate is convex on at leastpart of its upper surface to fit into the shape of the vertebrae.
 14. Anintervertebral disc prosthesis for substitution of a fibrocartilaginousdisc between adjacent vertebra in a spinal column comprising: an upperplate having a curved lower surface; a lower plate having an uppersurface; a core having an upper surface and a lower surface, the uppersurface of the core being curved and configured for contact with atleast part of the curved lower surface of the upper plate and the lowersurface of the core being configured for contact with at least part ofthe upper surface of the lower plate, said contact of the lower surfaceof the core with at least part of the upper surface of the lower platebeing configured for translation movements of the core with respect tothe lower plate along an axis substantially parallel to the uppersurface of the lower plate and for rotation movements of the core withrespect to the lower plate around an axis substantially perpendicular tothe upper surface of the lower plate when the intervertebral discprosthesis is assembled; and a stop comprising a male portion disposedon the lower plate and a female portion disposed on the core, the maleportion and the female portion each located along an edge of theprosthesis, and the male portion and the female portion each configuredto limit translation movements of the core with respect to lower plateand rotation movements of the core with respect to the lower plate, inwhich the male portion is a tag fixed by a dowel.
 15. An intervertebraldisc prosthesis according to claim 14 in which the upper surface of thecore is convex and the lower surface of the upper plate is concave, andthe lower surface of the core and the upper surface of the lower plateare each substantially planar.
 16. An intervertebral disc prosthesisaccording to claim 15 in which the upper plate has an upper surface thatis convex and the lower plate has a lower surface that is substantiallyplanar.
 17. An intervertebral disc prosthesis according to claim 16further comprising anchors configured to engage an adjacent vertebra.18. An intervertebral disc prosthesis according to claim 17 in which theanchors are disposed on opposite sides of the prosthesis.
 19. Anintervertebral disc prosthesis according to claim 14, in which thefemale portion is a recess.
 20. An intervertebral disc prosthesisaccording to claim 19 in which the recess is a groove.
 21. Anintervertebral disc prosthesis according to claim 14 in which the coreforms an acute angle in a front-rear direction.
 22. An intervertebraldisc prosthesis according to claim 14 in which the core can havedifferent thicknesses.
 23. An intervertebral disc prosthesis forsubstitution of a fibrocartilaginous disc between adjacent vertebra in aspinal column comprising: an upper plate having a curved lower surface;a lower plate having an upper surface; a core having an upper surfaceand a lower surface, the upper surface of the core being curved andconfigured for contact with at least part of the curved lower surface ofthe upper plate and the lower surface of the core being configured forcontact with at least part of the upper surface of the lower plate, saidcontact of the lower surface of the cote with at least part of the uppersurface of the lower plate being configured for translation movements ofthe core with respect to the lower plate along an axis substantiallyparallel to the upper surface of the lower plate and for rotationmovements of the core with respect to the lower plate around an axissubstantially perpendicular to the upper surface of the lower plate whenthe intervertebral disc prosthesis is assembled; and a stop comprising amale portion disposed on the lower plate and a female portion disposedon the core, the male portion and the female portion each located alongan edge of the prosthesis, and the male portion and the female portioneach configured to limit translation movements of the core with respectto lower plate and rotation movements of the core with respect to thelower plate, in which the male portion is an inwardly curved pin.
 24. Anintervertebral disc prosthesis according to claim 23 in which the uppersurface of the core is convex and the lower surface of the upper plateis concave, and the lower surface of the core and the upper surface ofthe lower plate are each substantially planar.
 25. An intervertebraldisc prosthesis according to claim 24 in which the upper plate has anupper surface that is convex and the lower plate has a lower surfacethat is substantially planar.
 26. An intervertebral disc prosthesisaccording to claim 25 further comprising anchors configured to engage anadjacent vertebra.
 27. An intervertebral disc prosthesis according toclaim 26 in which the anchors are disposed on opposite sides of theprosthesis.
 28. An intervertebral disc prosthesis according to claim 23in which the female portion is a recess.
 29. An intervertebral discprosthesis according to claim 28 in which the recess is a groove.
 30. Anintervertebral disc prosthesis according to claim 23 in which the coreforms an acute angle in a front-rear direction.
 31. An intervertebraldisc prosthesis according to claim 23 in which the core can havedifferent thicknesses.